1. Field of the Invention
The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the roller chain variety, which are used in engine timing applications as well as in industrial applications. The invention also has particular application to silent chains with block style lacing patterns.
2. Description of the Prior Art
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from the engine to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is know as "roller chain". A typical roller chain consists of interleaved, alternate inner links and outer links. The inner links, which are also know as "bushing" links, consist of spaced link plates, or sidebars, with bushings tightly received in openings, or apertures, at each end of the sidebars. The outer links consist of spaced link plates, or sidebars, with pins tightly received in openings, or apertures, at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are provided on the bushings, and when the roller chain is wrapped about a sprocket, the teeth of the sprocket are received between the laterally spaced sidebars and the longitudinally spaced rollers. An example of roller chain is found in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Roller chain drives can include both "true roller" and rollerless design. The true roller design includes the described rollers mounted about the bushings. Rollerless chain contains bushings that directly contact the sprocket. Both types of roller chain are typically specified in industry as British Standard chain and American National Standards Institute (ANSI) chain.
A second type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. Each link has a body with a pair of spaced apertures and the apertures of one set of links are arranged and aligned with the apertures of the next adjacent set of interleaved links. The links have a pair of depending toes separated by a crotch. The links are connected by pivot means, which are typically round pins received in the apertures. The pivot means can also be rocker joints, which consist of pins and rockers. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference. An example of silent chain which can be used in engine timing applications is found in U.S. Pat. No. 4,759,740, which is also incorporated herein by reference.
A conventional power transmission drive is comprised of either a silent chain or a roller chain wrapped about at least two sprockets supported by shafts. The chain is endless and assembled from interconnected links that are adaptable to fit over and about teeth formed on the sprockets. Movement of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket may be mounted on the engine crankshaft and the driven sprocket mounted on a valve camshaft. The rotation of the camshaft is thus controlled by the rotation of the crankshaft through the roller chain. Timing drive applications can also include the use of a power transmission chain in the camshaft to camshaft drive in an overhead camshaft engine.
The present invention relates to the control of the chain movement, specifically the prevention of back-bending of the chain. Typically, a chain tensioner or snubber or other external device is provided along the outside of the chain in order to control inward movement of the chain as it passes between the sprockets of the chain and sprocket assembly. The tensioner acts to control the chain by providing a load against the back surfaces of the chain links. The tensioner may be placed on either the tight side or the slack side of the chain.
The present invention seeks to provide control of the chain without the need for an external control such as a tensioner. Chain control is achieved by the use of extending butt portions on the links in order to prevent back-bending of the chain. Butt-style links have been used in the prior art in silent chains having bushings in the link apertures and, more recently, on the inverted tooth links in inverted tooth silent chains. The butts have typically been used to prevent excess rotation of the links and wear of the bushings within the link aperture.
The present invention is directed to a construction of a butt-style link for a roller chain. An embodiment of silent chain with block lacing is also described in which the butt-style links are utilized on the guide links.